Interference cancellation repeater

ABSTRACT

An interference cancellation repeater for canceling an interference signal included in an input signal including a first adaptive filter configured to generate a first estimated signal; a second adaptive filter configured to generate a second estimated signal; a first scaler configured to scale the first estimated signal based on a first scale factor determined according to a channel state; a second scaler configured to scale the second estimated signal based on a second scale factor determined according to the channel state; a first canceller configured to generate a first interference canceled signal based on the input signal and the scaled first estimated signal; and a second canceller configured to generate a second interference canceled signal based on the first interference canceled signal and the scaled second estimated signal.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 15/391,209 filed onDec. 27, 2016, which claims the benefit of Korean Patent Application No.10-2015-0187868, filed on Dec. 28, 2015, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein intheir entirety by reference.

BACKGROUND 1. Field

The inventive concept relates to an interference cancellation repeater.

2. Description of the Related Art

Since a common wireless repeater uses an identical frequency at itsinput terminal and output terminal, an output signal may be input to thewireless repeater again when an input antenna and an output antenna arenot sufficiently isolated from each other, and a multi-path signalgenerated by reflecting the output signal by an obstacle or a movingobject may be input to the wireless repeater again.

If the output signal is input to the wireless repeater again through afeedback channel as an interference signal, a signal quality maydeteriorate or the system may oscillate. Therefore, the wirelessrepeater is required to pre-process and repeat only an original inputsignal from which the interference signal has been canceled.

Therefore, an interference cancellation repeater has been used whichcancels a reflection interference signal and processes only an originalinput signal for output.

SUMMARY

The inventive concept is directed to an interference cancellationrepeater improving interference signal cancellation performance.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of the inventive concept, there is provided aninterference cancellation repeater for canceling an interference signalincluded in an input signal, the interference cancellation repeaterincludes: a first adaptive filter configured to generate a firstestimated signal; a second adaptive filter configured to generate asecond estimated signal; a first scaler configured to scale the firstestimated signal based on a first scale factor determined according to achannel state; a second scaler configured to scale the second estimatedsignal based on a second scale factor determined according to thechannel state; a first canceller configured to generate a firstinterference canceled signal based on the input signal and the scaledfirst estimated signal; and a second canceller configured to generate asecond interference canceled signal based on the first interferencecanceled signal and the scaled second estimated signal.

According to an exemplary embodiment, wherein the first interferencecanceled signal may be a signal which is generated by canceling somecomponents of the interference signal corresponding to the scaled firstestimated signal from the input signal, and the second interferencecanceled signal may be a signal which is generated by canceling at leastsome components of the interference signal corresponding to the scaledsecond estimated signal from the first interference canceled signal.

According to an exemplary embodiment, wherein the first and second scalefactors may be adaptively updated as the channel state changes.

According to an exemplary embodiment, wherein the first and second scalefactors may have different values.

According to an exemplary embodiment, wherein the first and second scalefactors may be each less than one.

According to an exemplary embodiment, the interference cancellationrepeater may further include a scaler controller configured to estimatethe channel state based on the input signal and an output signal of adigital filter for filtering the second interference canceled signal,and configured to generate the first and second scale factors accordingto the estimation result.

According to an exemplary embodiment, the interference cancellationrepeater may further include a digital filter configured to generate anoutput signal of a frequency band transmitted to a terminal by filteringthe second interference canceled signal.

According to an exemplary embodiment, wherein the first adaptive filtermay be configured to generate the first estimated signal based on thefirst interference canceled signal and the output signal, and the secondadaptive filter may be configured to generate the second estimatedsignal based on the second interference canceled signal and the outputsignal.

According to another aspect of the inventive concept, there is providedan interference cancellation repeater for canceling an interferencesignal included in an input signal, the interference cancellationrepeater includes: a first adaptive filter configured to generate afirst estimated signal; a second adaptive filter configured to generatea second estimated signal; a first scaler configured to scale the firstestimated signal based on a scale factor determined according to achannel state; a first canceller configured to generate a firstinterference canceled signal based on the input signal and the scaledfirst estimated signal; and a second canceller configured to generate asecond interference canceled signal based on the first interferencecanceled signal and the second estimated signal.

According to an exemplary embodiment, wherein the first interferencecanceled signal may be a signal which is generated by canceling somecomponents of the interference signal corresponding to the scaled firstestimated signal from the input signal, and the second interferencecanceled signal may be a signal which is generated by canceling at leastsome components of the interference signal corresponding to the secondestimated signal from the first interference canceled signal.

According to an exemplary embodiment, wherein the scale factor may beadaptively updated as the channel state changes.

According to an exemplary embodiment, wherein the scale factors may beless than one.

According to an exemplary embodiment, wherein the interferencecancellation repeater may further include a scaler controller configuredto estimate the channel state based on the input signal and an outputsignal of a digital filter for filtering the second interferencecanceled signal, and configured to generate the scale factor accordingto the estimation result,

According to an exemplary embodiment, wherein the interferencecancellation repeater may further include a digital filter configured togenerate an output signal of a frequency band transmitted to a terminalby filtering the second interference canceled signal.

According to an exemplary embodiment, wherein the first adaptive filtermay be configured to generate the first estimated signal based on thefirst interference canceled signal and the output signal, and the secondadaptive filter may be configured to generate the second estimatedsignal based on the second interference canceled signal and the outputsignal.

According to the inventive concept, a plurality of adaptive filters maybe stably operated while preventing deterioration in performance, andinterference signal cancellation performance can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of an interference cancellation repeateraccording to an example embodiment of the inventive concept;

FIG. 2 is a block diagram of an interference signal cancellation unitaccording to an example embodiment of the inventive concept;

FIG. 3 is a block diagram of an interference signal cancellation unitaccording to an example embodiment of the inventive concept; and

FIG. 4 is a flowchart of a method of canceling an interference signalaccording to an example embodiment of the inventive concept.

DETAILED DESCRIPTION

The inventive concept may be variously modified and have various exampleembodiments, so that specific example embodiments will be illustrated inthe drawings and described in the detailed description. However, thisdoes not limit the inventive concept to specific example embodiments,and it should be understood that the inventive concept covers all themodifications, equivalents and replacements included within the idea andtechnical scope of the inventive concept.

In describing the inventive concept, in the following description, adetailed explanation of known related technologies may be omitted toavoid unnecessarily obscuring the subject matter of the inventiveconcept. In addition, numeral figures (for example, 1, 2, and the like)used during describing the specification are just identification symbolsfor distinguishing one element from another element.

Further, in the specification, if it is described that one component is“connected” or “accesses” the other component, it is understood that theone component may be directly connected to or may directly access theother component but unless explicitly described to the contrary, anothercomponent may be “connected” or “access” between the components.

In addition, terms including “unit”, “er”, “or”, “module”, and the likedisclosed in the specification mean a unit that processes at least onefunction or operation and this may be implemented by hardware orsoftware such as a processor, a micro processor, a micro controller, acentral processing unit (central processing unit), a graphics processingunit (GPU), an accelerated Processing unit (APU), a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), anda field programmable gate array (FPGA) or a combination of hardware andsoftware.

Moreover, it is intended to clarify that components in the specificationare distinguished in terms of primary functions of the components. Thatis, two or more components to be described below may be provided to becombined to one component or one component may be provided to be dividedinto two or more components for each more subdivided function. Inaddition, each of the respective components to be described below mayadditionally perform some or all functions among functions which othercomponents take charge of in addition to a primary function which eachcomponent takes charge of and some functions among the primary functionswhich the respective components take charge of are exclusively chargedby other components to be performed, of course.

Hereinafter, example embodiments of the inventive concept will bedescribed in detail.

FIG. 1 is a block diagram of an interference cancellation repeater 100according to an example embodiment of the inventive concept.

Referring to FIG. 1, the interference cancellation repeater 100according to an example embodiment of the inventive concept may repeatcommunication between a base station and a terminal.

The interference cancellation repeater 100 may include a radio frequency(RF) receiver 110, an analog-to-digital (A/D) converter 120, aninterference signal cancellation unit 130, a digital-to-analog (D/A)converter 140, and an RF transmitter 150.

Describing a downlink path as an example, the RF receiver 110 mayreceive an RF signal from a base station. Furthermore, the RF receiver110 may receive all or some of an output signal (for example, a repeatsignal) transmitted from the RF transmitter 150 in addition to the RFsignal. The output signal transmitted from the RF transmitter 150 inaddition to the RF signal may function as an interference signal to theRF signal.

The analog-to-digital converter 120 may convert the RF signal to adigital signal.

The interference signal cancellation unit 130 may cancel an interferencesignal included in the digital signal. For example, the interferencesignal cancellation unit 130 may generate an inverse-phase estimatedsignal corresponding to the interference signal included in the digitalsignal using a plurality of adaptive filters and may add the generatedestimated signal to the digital signal to cancel the interferencesignal.

The digital-to-analog converter 140 may convert the digital signal fromwhich the interference signal has been canceled to an analog signal,that is, an original RF signal.

The RF transmitter 150 may transmit the RF signal to the outside afterprocessing such as amplification. For example, the RF transmitter 150may transmit the amplified RF signal to a terminal.

As described above, the interference cancellation repeater 100 accordingto an example embodiment of the inventive concept may cancel aninterference signal included in an input signal using the interferencesignal cancellation unit 130. A specific operation of the interferencesignal cancellation unit 130 will be described in detail later belowwith reference to referring to FIG. 2.

FIG. 2 is a block diagram of an interference signal cancellation unit130 according to an example embodiment of the inventive concept.

Referring to FIG. 2, the interference signal cancellation unit 130according to an example embodiment of the inventive concept may includefirst through n^(th) cancellers 131-1 through 131-n (where n is anatural number of 3 or more), a digital filter 133, first through n^(th)adaptive filters 135-1 through 135-n, first through n^(th) scalers 137-1through 137-n, and a scaler controller 139. However, the inventiveconcept is not limited thereto. The interference signal cancellationunit 130 may include two adaptive filters and a canceller and a scalercorresponding to each of the two adaptive filters. Also, depending on anexample embodiment, the interference signal cancellation unit 130 mayhave a smaller number of scalers than the number of adaptive filters.

Hereinafter, for convenience of description, it is assumed that theinterference signal cancellation unit 130 includes the first adaptivefilter 135-1, the second adaptive filter 135-2, and the n^(th) adaptivefilter 135-n, and the number of cancellers and scalers is also n,corresponding to the number of the adaptive filters.

A first canceller 131-1 may generate a first interference canceledsignal by combining an input signal and a scaled first estimated signal.For example, the input signal may refer to a signal transmitted from theanalog-to-digital converter 120 (see FIG. 1). Here, it is assumed thatthe input signal is a digital signal including an RF signal and aninterference signal. The interference signal included in the inputsignal may be partially canceled by combining the scaled first estimatedsignal and the input signal. Here, the fact that the interference signalincluded in the input signal is partially canceled means that amagnitude of at least some components corresponding to the scaled firstestimated signal among various components of the interference signal isreduced or becomes zero. A ratio of the interference signal canceled bythe first canceller 131-1 to the entire interference signal maycorrespond to a degree of scaling of the first scaler 137-1 describedlater below.

A second canceller 131-2 may generate a second interference canceledsignal by combining the first interference canceled signal and a scaledsecond estimated signal. An interference signal included in the firstinterference canceled signal may be further partially canceled bycombining the scaled second estimated signal and the first interferencecanceled signal. Here, the fact that the interference signal included inthe first interference canceled signal is further partially canceledmeans that a magnitude of at least some components corresponding to thescaled second estimated signal among various components of theinterference signal included in the first interference canceled signalis reduced or becomes zero. A ratio of the interference signal canceledby the second canceller 131-2 to the entire interference signal maycorrespond to a degree of scaling of the second scaler 137-2 describedlater below.

The n^(th) canceller 131-n may generate an n^(th) interference canceledsignal by combining an n−1^(th) interference canceled signal (in anexample of FIG. 2, a second interference canceled signal when n is 3)and a scaled n^(th) estimated signal. The remaining interference signalincluded in the n−1^(th) interference canceled signal may be completelycanceled by combining the n−1^(th) interference canceled signal and thescaled n^(th) estimated signal. Here, the fact that the remaininginterference signal included in the second interference canceled signalis completely canceled means that a magnitude of each of variouscomponents of the interference signal is reduced to 0, that is, all ofthe components are canceled. A ratio of the interference signal canceledby n^(th) canceller 131-n to the entire interference signal maycorrespond to a degree of scaling of the n^(th) scaler 137-n describedlater below.

The digital filter 133 may filter the n^(th) interference canceledsignal transmitted from the n^(th) canceller 131-n. Here, the filteringmay be understood as a process of digital signal processing, forexample, a signal processing process for canceling at least onefrequency band outside a specific frequency band for transmission to theterminal from the n^(th) interference canceled signal.

The n^(th) interference canceled signal filtered by the digital filter133 may be transmitted to the first adaptive filter 135-1, and thesecond adaptive filter 135-2 through the n^(th) adaptive filter 135-n.In one aspect, it will understood that an output signal of the digitalfilter 133 is fed back to the first adaptive filter 135-1, and thesecond adaptive filter 135-2 through the n^(th) adaptive filter 135-n.

Meanwhile, although not shown in FIG. 2, a delay unit may further beprovided between the digital filter 133 and at least one of the firstthrough n^(th) adaptive filters 135-1 through 135-n.

The first adaptive filter 135-1 may generate a first estimated signalusing a signal fed back from the digital filter 133, that is, the outputsignal of the digital filter 133 and an output of the first canceller131-1, that is, a first interference canceled signal. For example, thefirst estimated signal may be a signal obtained by estimating at leastsome of the interference signal included in the input signal.

The first scaler 137-1 may scale the first estimated signal based on afirst scale factor that is transmitted from the scaler controller 139and indicates a scale ratio allocated for the first estimated signalaccording to a channel state, and thus the scaled first estimated signalmay be generated. As a scale of the first estimated signal is adjusted,only some of the interference signal included in the input signal may becanceled by the first canceller 131-1 at a certain rate.

The second adaptive filter 135-2 may generate a second estimated signalusing the output signal of the digital filter 133 and an output of thesecond canceller 131-2, that is, a second interference canceled signal.For example, the second estimated signal may be a signal obtained byestimating at least some of an interference signal included in thesecond interference canceled signal.

The second scaler 137-2 may scale the second estimated signal based on asecond scale factor that is transmitted from the scaler controller 139and indicates a scale ratio allocated for the second estimated signalaccording to the channel state, and thus the scaled second estimatedsignal may be generated. As a scale of the second estimated signal isadjusted, only some of the interference signal included in the firstinterference canceled signal may be canceled by the second canceller131-2 at a certain rate.

The n^(th) adaptive filter 135-n may generate an n^(th) estimated signalusing the output signal of the digital filter 133. For example, then^(th) estimated signal may be a signal obtained by estimating at leastsome of an interference signal included in the n−1^(th) interferencecanceled signal.

The n^(th) scaler 137-n may scale the n^(th) estimated signal based onan n^(th) scale factor that is transmitted from the scaler controller139 and indicates a scale ratio allocated for the n^(th) estimatedsignal according to the channel state, and thus the scaled n^(th)estimated signal may be generated. According to an example embodiment,when the n^(th) estimated signal is a signal generated for cancelinginterference signals in the last order, the n^(th) scale factor may beset such that all interference signals included in the n−1^(th)interference canceled signal are canceled by the n^(th) canceller 131-nwith the scaled n^(th) estimated signal.

Meanwhile, the first through n^(th) adaptive filters 135-1 through 135-nmay be implemented by a least mean square (LMS) filter. A detailedoperation of the LMS filter is obvious to those of ordinary skilled inthe art, and thus, a detailed description thereof will not be givenherein. It is apparent that types of adaptive filters that can beimplemented according to an example embodiment of the inventive conceptdo not limit the technical scope of the inventive concept.

The scaler controller 139 may estimate the channel state based on theinput signal and the output signal of the digital filter 133. Forexample, the scaler controller 139 may calculate a magnitude ratiobetween the input signal and the output signal, and may estimate thechannel state, for example, whether a magnitude of a signal inputthrough the channel is changed, or whether the signal is faded. AlthoughFIG. 2 shows that the scaler controller 139 estimates the channel statebased on the input signal and the output signal, the inventive conceptis not limited thereto. The scaler controller 139 may receive an outputof the n^(th) canceller 131-n, that is, the n^(th) interference canceledsignal, and may estimate the channel state based on the input signal andthe n^(th) interference canceled signal.

The scaler controller 139 may generate the first through n^(th) scalefactors according to the channel state estimation result. The scalercontroller 139 may generate the first through n^(th) scale factors suchthat scale ratios of the first through the n^(th) estimated signals aredifferent from each other. For example, the scaler controller 139 maygenerate the first through n^(th) scale factors such that the scaleratios gradually decrease in the order of the first through n^(th)estimated signals or vice versa. In addition, the scaler controller 139may generate the first through n^(th) scale factors in variouscombinations. Each of the first through n^(th) scale factors may be lessthan one.

The scaler controller 139 may adaptively update the first through n^(th)scale factors according to the channel state estimation result. It isfor ensuring performance of the first through n^(th) adaptive filters135-1 through 135-n in response to a change of the channel state.

As described above, the interference signal cancellation unit 130according to an example embodiment of the inventive concept maycompletely cancel an interference signal from an input signal using aplurality of adaptive filters. The interference signal cancellation unit130 adjusts a magnitude of an interference signal to be estimated of theadaptive filters so as not to cause performance degradation of theadaptive filters in response to a change of the channel state so thatperformance of the adaptive filters may be maintained in an optimumstate, and cancellation performance of the interference signal may beimproved.

FIG. 3 is a block diagram of an application example of an interferencecancellation repeater according to an example embodiment of theinventive concept. The interference signal cancellation unit 230 of FIG.3 shows an application example in which it is assumed that theinterference signal cancellation unit 230 has two cancellers and twoadaptive filters and one scaler. In FIG. 3, like elements as those ofFIG. 2 are denoted by the same reference numerals, and descriptionsthereof will be omitted.

A first canceller 231-1 may generate a first interference canceledsignal by combining an input signal and a scaled first estimated signal.The interference signal included in the input signal may be partiallycanceled by combining the scaled first estimated signal and the inputsignal.

A second canceller 231-2 may combine the first interference canceledsignal and a second estimated signal to generate a second interferencecanceled signal. The interference signal included in the firstinterference canceled signal may be completely canceled by combining thesecond estimated signal and the first interference canceled signal.

A digital filter 233 may filter the second interference canceled signaltransmitted from the second canceller 231-2. The second interferencecanceled signal filtered by the digital filter 233 may be fed back to afirst adaptive filter 235-1 and a second adaptive filter 235-2.

The first adaptive filter 235-1 may generate the first estimated signalusing a signal fed back from the digital filter 233 and the firstinterference canceled signal. For example, the first estimated signalmay be a signal obtained by estimating at least some of the interferencesignal included in the input signal.

The first scaler 237-1 may scale the first estimated signal based on ascale factor that is transmitted from the scaler controller 239 andindicates a scale ratio allocated for the first estimated signalaccording to a channel state, and thus the scaled first estimated signalmay be generated. As a scale of the first estimated signal is adjusted,only some of the interference signal included in the input signal may becanceled by the first canceller 231-1 at a certain rate.

The second adaptive filter 235-2 may generate the second estimatedsignal using the signal fed back from the digital filter 233 and thesecond interference canceled signal. For example, the second estimatedsignal may be a signal obtained by estimating at least some of theinterference signal included in the first interference canceled signal.

In the interference signal cancellation unit 230 according to an exampleembodiment of the inventive concept, the second adaptive filter 235-2may not be connected to a scaler unlike the first adaptive filter 235-1.If a magnitude of a signal to be estimated by the second adaptive filter235-2, that is, a magnitude of the interference signal included in thefirst interference canceled signal does not cause deterioration of thesecond adaptive filter 235-2, then a scaler corresponding to theadaptive filter 235-2 may be omitted.

FIG. 4 is a flowchart of a method of canceling an interference signalaccording to an example embodiment of the inventive concept. In someexample embodiments, it should be noted that each of operations shown inFIG. 4 may be performed out of the order shown. For example,successively illustrated operations may be performed substantiallyconcurrently or in a reverse order. The method of canceling aninterference signal of FIG. 4 may be performed by the interferencecancellation units 130 and 230 described with reference to FIGS. 1through 3. Hereinafter, a case where the method of canceling aninterference signal is performed by the interference cancellation unit130 will be described as an example.

Referring to FIG. 4, in operation S410, the digital filter 133 maygenerate an output signal by filtering a signal which is generated bycompletely canceling an interference signal from an input signal. Theoutput signal of the digital filter 133 may be fed back to the firstthrough n^(th) adaptive filters 135-1 through 135-n.

In operation S420, each of the first through n^(th) adaptive filters135-1 through 135-n may generate an estimated signal based on the outputsignal. The first adaptive filter 135-1 may generate a first estimatedsignal based on the output signal and the input signal. The firstestimated signal may be an estimated signal to cancel an interferencesignal included in the input signal. The second adaptive filter 135-2may generate a second estimated signal based on the output signal andthe first interference canceled signal. The second estimated signal maybe an estimated signal to cancel the interference signal included in thefirst interference canceled signal. The n^(th) adaptive filter 135-n maygenerate an n^(th) estimated signal based on the output signal and ann−1^(th) interference canceled signal. The n^(th) estimated signal maybe an estimated signal to cancel an interference signal included in then−1^(th) interference canceled signal.

In operation S430, the first through n^(th) scalers 137-1 through 137-nmay scale an estimated signal output from a corresponding adaptivefilter according to a corresponding scale factor. The first scaler 137-1may scale the first estimated signal based on a first scale factor, thesecond scaler 137-2 may scale the second estimated signal based on asecond scale factor, and the n^(th) scaler 137-n may scale the n^(th)estimated signal based on an n^(th) scale factor.

In operation S440, the first through n^(th) cancellers 131-1 through131-n may sequentially cancel some of an interference signal usingcorresponding estimated signals, respectively. The first canceller 131-1may combine the input signal and the scaled first estimated signal tocancel some of the interference signal, and then may output the firstinterference canceled signal. The second canceller 131-2 may combine thefirst interference canceled signal and the scaled second estimatedsignal to cancel another part of the interference signal, and then mayoutput the second interference canceled signal. Finally, the n^(th)canceller 131-n may combine the n−1^(th) interference canceled signaland the scaled n^(th) estimated signal to cancel the rest of theinterference signal, and then may finally output the n^(th) interferencecanceled signal.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope of the disclosure as defined by thefollowing claims.

What is claimed is:
 1. An interference cancellation repeater forcanceling an interference signal included in an input signal, theinterference cancellation repeater comprising: a first adaptive filterconfigured to generate a first estimated signal based on a firstinterference canceled signal and an output signal of the interferencecancellation repeater; a second adaptive filter configured to generate asecond estimated signal based on a second interference canceled signaland the output signal; a scaler configured to scale the second estimatedsignal based on a scale factor determined according to a channel state;a first canceller configured to generate the first interference canceledsignal based on the input signal and the first estimated signal; and asecond canceller configured to generate the second interference canceledsignal based on the first interference canceled signal and the scaledsecond estimated signal.
 2. The interference cancellation repeater ofclaim 1, wherein the first interference canceled signal is a signalwhich is generated by canceling some components of the interferencesignal corresponding to the first estimated signal from the inputsignal, and the second interference canceled signal is a signal which isgenerated by canceling at least some components of the interferencesignal corresponding to the scaled second estimated signal from thefirst interference canceled signal.
 3. The interference cancellationrepeater of claim 1, wherein the scale factor is adaptively updated asthe channel state changes.
 4. The interference cancellation repeater ofclaim 1, wherein the scale factor is less than one.
 5. The interferencecancellation repeater of claim 1, further comprising: a scalercontroller configured to estimate the channel state based on the inputsignal and the output signal, and generate the scale factor according tothe estimated channel state.
 6. The interference cancellation repeaterof claim 1, further comprising: a digital filter configured to generatethe output signal transmitted to a terminal by filtering the secondinterference canceled signal.
 7. A method for canceling an interferencesignal of an interference cancellation repeater, the method comprising:generating a first estimated signal based on a first interferencecanceled signal and an output signal of the interference cancellationrepeater; generating a second estimated signal based on a secondinterference canceled signal and the output signal; and scaling thesecond estimated signal based on a scale factor determined according toa channel state, wherein the first interference canceled signal isgenerated based on an input signal and the first estimated signal, andwherein the second interference canceled signal is generated based onthe first interference canceled signal and the scaled second estimatedsignal.
 8. The method of claim 7, wherein the first interferencecanceled signal is generated by canceling some components of theinterference signal corresponding to the first estimated signal from theinput signal, and the second interference canceled signal is generatedby canceling at least some components of the interference signalcorresponding to the scaled second estimated signal from the firstinterference canceled signal.
 9. The method of claim 7, wherein thescale factor is adaptively updated as the channel state changes.
 10. Themethod of claim 7, wherein the scale factor is less than one.
 11. Themethod of claim 7, further comprising: estimating the channel statebased on the input signal and the output signal; and generating thescale factor according to the estimated channel state.
 12. The method ofclaim 7, further comprising generating the output signal transmitted toa terminal by filtering the second interference canceled signal.